This invention relates generally to seals and more particularly to radial seals formed of fluorocarbon resin which are usable, for example, as an oil seal, exerting radial sealing pressure to retain liquid or gaseous fluid and/or exclude foreign matter, and methods of making such radial seals.
In general, radial seals such as oil seals are required to meet the following conditions: (1) First, they should exhibit satisfactory resistances to wear, heat and pressure and other physical properties generally required of a sealing device and additionally substantial chemical, corrosion and fungus resistances as well as satisfactory durability. (2) Secondly, they should at all times have a good followability, that is, an ability to closely follow the mating surface of a rotating shaft or other member to be sealed for good elastic sealing contact therewith and be capable of serving the intended sealing function for an extended period of service.
As for seal materials, among others, fluorocarbon resin is known to meet the requirements stated above in (1) and seal units including a sealing element formed of this sort of resin material have previously been in use. For example, a seal unit has been proposed which includes at least one sealing element formed of fluorocarbon resin and including, as illustrated in FIG. 10 of the accompanying drawings, a lip portion r and a flange portion f which is formed integral therewith and clamped by metallic case means m.
Though such seal unit generally satisfies the requirements stated above in (1), its sealing performance has been unsatisfactory in that the lip portion r of its sealing element exhibits only a limited ability to follow the mating surface of a rotating shaft or the like member to be sealed. In a proposal previously made to overcome this difficulty, the lip portion r' of the sealing element formed of fluorocarbon resin is lined over the outside surface thereof with an appropriate elastomeric material e by heat-bonding, as shown in FIG. 11, and an annular, garter spring s is fitted to the elastomeric lining e around the periphery thereof in order to improve the sealing characteristics and particularly the followability of the seal lip portion relative to the mating member to be sealed.
Even with such improved form of seal unit, however, the advantageous characteristics of fluorocarbon resin, of which the sealing element is formed, cannot be fully utilized because of the use of lining e formed of an elastomeric material which is generally inferior to fluorocarbon resin in resistance to chemicals, corrosion and fungi. In addition, the extra labor needed for the heat-bonding of elastomeric material e on the sealing element obviously involves an increase in cost of production and the exposed garter spring, metallic in nature, is liable to loss of durability under the influence of any liquid adhering thereto. On account of these disadvantages, it has been practically impossible even with this form of seal unit to obtain any fully satisfactory results.